The invention relates to photonic devices. As used herein, the designation xe2x80x9cphotonic devicexe2x80x9d is intended to apply to all kinds of devices whose operation involves photons. Exemplary of such devices are optoelectronic devices, integrated optics devices, optical waveguides, photonic integrated circuits, and the like. Also, the designation xe2x80x9cphotonic devicexe2x80x9d is intended to apply to any intermediate products obtained in the manufacture of such devices: exemplary of such intermediate products are so-called xe2x80x9claser barsxe2x80x9d or xe2x80x9coptical amplifier barsxe2x80x9d from which individual semiconductor laser sources or amplifiers are produced by segmenting such bars.
More specifically, the invention deals with a technique for treating end facets in photonic devices.
Photonic devices such as semiconductor lasers or semiconductor optical amplifiers may need coatings on their end facets in order permit proper operation. For instance, semiconductor lasers are produced from laser bars having opposed first and second major surfaces with similarly opposed end facets extending between and orthogonally to the major surfaces. Electrically conductive strips in the form of metalisations extending between the end facets of the laser bar are already provided at given distances on the first or upper major surface of the laser bar. Each such metalisation is intended to define a respective lasing cavity whose end mirrors are defined by the end facets.
Treatment of these end facets typically involves deposition of one or more coating layers having reflection-modifying properties. Coating is usually effected by resorting to e-gun deposition technology in a vacuum chamber. In the case of laser manufacturing, after such coatingxe2x80x94and additional treatment(s) as possibly requiredxe2x80x94the laser bar is fragmented into a plurality of individual laser dice, each having a respective contact metalisation at its upper surface and intended to constitute an individual laser device.
All of the foregoing corresponds to standard technology and, as such, does not require to be described in greater detail herein.
The required treatment (e.g. coating) must be limited to the end facets. For instance, in the case of a laser bar, deposition of the coating material on the major surfaces of the laser bar is highly undesirable and must be avoided as this may adversely affect further manufacturing steps and, more generally, operation and reliability of the final product.
Obviously, no unwanted coating may take place on those surfaces eventually intended to represent the xe2x80x9clateralxe2x80x9d faces of each individual laser (or amplifier) device produced from the bar: those lateral surfaces are in fact exposed only as a result of the bar (already coated at its end facets) being segmented into single devices.
Masking techniques are well known and might be resorted to in photonic device technology when a certain surface must be protected from undesired deposition/treatment. However, these known techniques are not truly attractive when considered for use in the scenario outlined in the foregoing: this is primarily due to the very small dimensions of the components to be treated, that make such components inherently difficult to handle. Also, some of these techniques may adversely affect the quality of the final product, e.g. by leading to unwanted contamination of the facets being treated.
xe2x80x9cMechanicalxe2x80x9d masking of those surfaces that must be excluded from the coating process may thus be preferred. This may occur by means of xe2x80x9cdummyxe2x80x9d bars or plates. Precise positioning of those masking bodies becomes however a quite critical factor. For instance, bars currently used for manufacturing semiconductor lasers for optical communications are in the form of rectangular bars having a width in the range of 300 microns or less and a height of 100 microns or less. Even very small misalignments in the masking arrangement may thus be detrimental to the result in the coating process as these may lead e.g. to unwanted xe2x80x9cshadowingxe2x80x9d and xe2x80x9coversprayxe2x80x9d phenomena. Also, mechanical masking techniques may require very delicate handling of the device or product being treated and/or may not be suitable to be automated, thus adversely affecting productivity of the coating process and manufacturing process at large.
The object of the present invention is thus to provide an improved solution that overcomes the drawbacks of prior art techniques outlined in the foregoing. According to the present invention, such an object is achieved by means of a method having the features set forth in the claims that follow. The invention also relates to a carrier for carrying out such a method.